rotate an object while it follows a path
One way to do this is with an empty following the orbit. This way you can parent an object to the empty and rotate it independently:


Add an empty and make it follow a path (e.g. with the Follow Path constraint). Clicking Animate Patch will automatically add an fcurve modifier which endlessly moves the empty along the path:



To control the orbit speed, set the total number of frames required for an orbit by adjusting the Frames value in Properties > Object data > Path Animation with the curve selected:


Parent your object to the empty (&#9096; CtrlP):



Now the object's transforms will be relative to the empty. You can rotate the empty to tilt the object's axis of rotation if you like.
Make the planet object spin. To do this, insert a keyframe on the Z rotation of the object ( RMB > Insert single keyframe). You'll only need this one keyframe. You could use drivers instead, however that may cause issues if you plan on using a renderfarm such as sheepit.

In the graph editor, add a Generator fcurve modifier. Note that internally blender stores rotations as radians, so to make the planet rotate once every 26 frames, you'll want the X multiplier to be 6.28318531/26 (6.28318531 radians = 360°).




Result: